The reported association between an unfavorable fetal environment and adult diseases may be confounded by a genetic predisposition toward specific diseases (eg, vascular diseases) as the maternal genes that are transmitted o the fetus may also set the uterine environment. Epidemiological studies may not differentiate between the unfavorable uterine environment vs the hereditary predisposition common to mother and fetus. As endothelial nitric oxide synthase (NOS3) is important in determining vascular function in adults, and deficiency in its function leads to abnormal vascular adaptations in pregnancy and an unfavorable fetal environment, we crossbred transgenic mice lacking a functional NOS3 gene (NOS3-/-KO) and their wild-type control (NOS3+/+WT) to clarify the roles of the fetal environment vs genetics in determining adult vascular function. Our preliminary results show that the vascular phenotype in heterozygous adult that inherit the functional NOS3 allele from the father and therefore develop in NOS3-/-KO mothers (NOS3+Pat/-Mat) is similar to NOS3-/-KO mice. In contrast, the vascular phenotype in heterozygous adults that inherit the father's nonfunctional NOS3 allele and develop in NOS3+/+WT mothers (NOS3+Mat/-Pat) is similar to NOS3+/+WT mice. We hypothesize that the observed difference between the heterozygous mice is due to fetal programming caused by an unfavorable uterine environment resulting from altered vascular adaptations in the NOS3-/-KO pregnancy secondary to lack of NOS3 function. To test this hypothesis, we propose the following aims: 1) determine vascular function and blood pressure in adult offspring born to NOS3-/-KO females bred with NOS3-/-KO or NOS3+/+WT males, and compare them to offspring of NOS3+/+WT females bred with NOS3-/-KO or NOS3+/+WT males; 2) determine the roles of uterine environment vs genetics by comparing the vascular phenotype in later life in NOS3-+Pat/-Mat, NOS3+Mat/-Pat, NOS3-/-KO and NOS3+/+WT embryos transferred into NOS3-/-KO surrogate mothers to those transferred into NOS3+/+WT surrogate mothers; 3) determine the transgenerational consequences of fetal programming by examining the vascular phenotype in NOS3+Pat/-Mat, NOS3+Mat/-Pat, NOS3-/-KO and NOS3+/+WT during pregnancy (aim 3a), as well as in their offspring in adult life (aim 3b); 4) compare adult vascular phenotype between NOS3+Pat/-Mat , NOS3+Mat/-Pat, NOS3-/-KO and NOS3+/+WT offspring born to the same dams in the 1st, 2nd, and 5th pregnancies: This unique model is relevant to adverse pregnancy outcomes related to abnormal uterine environment, such as preeclampsia and fetal growth restriction, and has significant implications regarding the long-term health of offspring.